js ul li 悬浮菜单

<ul class="menu">
  <li><a href="#">Home</a></li>
  <li><a href="#">About</a></li>
  <li><a href="#">Services</a>
    <ul class="submenu">
      <li><a href="#">Web Design</a></li>
      <li><a href="#">SEO</a></li>
    </ul>
  </li>
  <li><a href="#">Contact</a></li>
</ul>

.menu {
  list-style-type: none;
  padding: 0;
  display: flex;
}

.menu li {
  position: relative;
}

.menu a {
  display: block;
  padding: 10px 20px;
  text-decoration: none;
  color: #333;
}

.menu li:hover .submenu {
  display: block;
}

.submenu {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  background-color: #fff;
  border: 1px solid #ccc;
  list-style-type: none;
  padding: 0;
  min-width: 150px;
}

.submenu li {
  width: 100%;
}

.submenu a:hover {
  background-color: #f0f0f0;
}

document.querySelectorAll('.menu > li').forEach(li => {
  li.addEventListener('mouseenter', () => {
    const submenu = li.querySelector('.submenu');
    if (submenu) {
      submenu.style.display = 'block';
    }
  });
  li.addEventListener('mouseleave', () => {
    const submenu = li.querySelector('.submenu');
    if (submenu) {
      submenu.style.display = 'none';
    }
  });
});